The 3GPP (3rd generation partnership project) is a project that examines and prepares specifications of a mobile communication system based on a network in which W-CDMA (Wideband-code division multiple access) and GSM (Global system for mobile communications). In the 3GPP, W-CDMA system is standardized as the third generation cellular mobile communication system, and its services have been successively started. HSDPA (High-speed downlink packet access) in which a communication speed is further increased is also standardized, and its services are started. In the 3GPP, the evolution of the third generation radio access technology (hereinafter referred to as “LTE (long term evolution” or “EUTRA (evolved universal terrestrial radio access)”) and a broadband frequency band are utilized, and thus a mobile communication system for realizing the highspeed transmission and reception of data (hereinafter referred to as an “LTE-A (long term evolution-advanced” or an “advanced-EUTRA”) is being examined.
As the communication system in the LTE, an OFDMA (orthogonal frequency division multiple access) system in which subcarriers orthogonal to each other are used to perform user multiplexing and an SC-FDMA (single carrier-frequency division multiple access) system are being examined. Specifically, in a downlink, the OFDMA system which is a multi-carrier communication system is proposed, and, in an uplink, the SC-FDMA system which is a single-carrier communication system is proposed.
On the other hand, as the communication system in the LTE-A, in a downlink, the introduction of the OFDMA system is being examined, and, in an uplink, in addition to the SC-FDMA system, the introduction of the OFDMA system and a clustered-SC-FDMA (clustered-single carrier-frequency division multiple access, also referred to as DFTs-OFDM with spectrum division control) system is being examined. Here, in the LTE and the LTE-A, the SC-FDMA system proposed as an uplink communication system has the feature of being able to reduce a PAPR (peak to average power ratio: transmit power) when data is transmitted.
Whereas a frequency band used in a general mobile communication system is contiguous, in the LTE-A, it is examined that a plurality of contiguous/discontiguous frequency bands (hereinafter referred to as a “carrier element, carrier component (CC)” or an “element carrier, component carrier (CC)”) are used in a composite manner and are managed as one broadband frequency band (frequency band aggregation: also referred to as spectrum aggregation, carrier aggregation, frequency aggregation or the like) (non-patent document 1). Furthermore, it is also proposed that, in order for a base station apparatus and a mobile station apparatus to more flexibly use a broadband frequency band to perform communications, a frequency band used in a downlink communication and a frequency band used in an uplink communication are made to have different frequency bandwidths (asymmetric frequency band aggregation: asymmetric carrier aggregation) (non-patent document 2).
FIG. 7 is a diagram illustrating a mobile communication system on which frequency band aggregation has been performed in a conventional technology. That, as shown in FIG. 7, a frequency band used in downlink (hereinafter also referred to as DL) communication and a frequency band used in uplink (hereinafter also referred to as UL) communication are made to have the same bandwidth is also referred to as symmetric frequency band aggregation (symmetric carrier aggregation). As shown in FIG. 7, a base station apparatus and a mobile station apparatus use a plurality of carrier elements that are a contiguous and/or discontiguous frequency band in a composite manner, and thereby can perform communications in a broadband frequency band composed of a plurality of carrier elements. FIG. 7 shows, as an example, that a frequency band (hereinafter also referred to as a DL system band, a DL system bandwidth) used in downlink communication having a 100 MHz bandwidth is composed of five downlink carrier elements (DCC1: downlink component carrier 1, DCC2, DCC3, DCC4 and DCC 5) each having a 20 MHz bandwidth. FIG. 7 also shows, as an example, that a frequency band (hereinafter also referred to as a UL system band, a UL system bandwidth) used in uplink communication having a 100 MHz bandwidth is composed of five uplink carrier elements (UCC1: uplink component carrier 1, UCC2, UCC3, UCC4 and UCC 5) each having a 20 MHz bandwidth.
In FIG. 7, in each of the downlink carrier elements, downlink channels such as a physical downlink control channel (hereinafter referred to as a PDCCH) and a physical downlink shared channel (hereinafter referred to as a PDSCH) are allocated. The base station apparatus can use the PDCCH to transmit, to the mobile station apparatus, control information (resource assignment information, MCS (modulation and coding scheme) information, HARQ (hybrid automatic repeat request) processing information and the like) for transmitting a downlink transport block transmitted using the PDSCH, and can use the PDSCH to transmit the downlink transport block to the mobile station apparatus. In other words, in FIG. 7, the base station apparatus can transmit up to five downlink transport blocks at the maximum to the mobile station apparatus in the same subframe.
In each of the uplink carrier elements, uplink channels such as a physical uplink control channel (hereinafter referred to as a PUCCH) and a physical uplink shared channel (hereinafter referred to as a PUSCH) are allocated. The mobile station apparatus can use the PUCCH and/or the PUSCH to transmit, to the base station apparatus, control information of HARQ for the PDCCH and/or the downlink transport block (hereinafter also referred to as control information of HARQ). Here, the control information of HARQ refers to information (signal) indicating ACK/NACK (positive acknowledgment/negative acknowledgment) and/or information (signal) indicating DTX (discontiguous transmission). The information indicating the DTX refers to information indicating that the mobile station apparatus cannot detect the PDCCH transmitted from the base station apparatus. Here, in FIG. 7, there may be a downlink/uplink carrier element where any of downlink/uplink channels such as the PDCCH, the PDSCH, the PUCCH and the PUSCH is not allocated.
Likewise, FIG. 8 is a diagram illustrating a mobile communication system on which asymmetric frequency band aggregation (asymmetric carrier aggregation) has been performed in the conventional technology. As shown in FIG. 8, in the base station apparatus and the mobile station apparatus, the frequency band used in the downlink communication and the frequency band used in the uplink communication are made to have different bandwidths, carrier elements which are a contiguous and/or discontiguous frequency band constituting these frequency bands are used in a composite manner and thus communications can be performed in a broadband frequency band. FIG. 8 shows, as an example, that a frequency band used in the downlink communication having a 100 MHz bandwidth is composed of five downlink carrier elements (DCC1, DCC2, DCC3, DCC4 and DCC 5) each having a 20 MHz bandwidth. FIG. 7 also shows that a frequency band used in the uplink communication having a 40 MHz bandwidth is composed of two uplink carrier elements (UCC1 and UCC 2) each having a 20 MHz bandwidth. In FIG. 8, in each of the downlink/uplink carrier elements, downlink/uplink channels are allocated, and the base station apparatus can use a plurality of PDSCHs assigned by a plurality of PDCCHs, to transmit a plurality of downlink transport blocks to the mobile station apparatus in the same subframe. The mobile station apparatus can use the PUCCH and/or the PUSCH to transmit control information of HARQ to the base station apparatus.    Non-patent document 1: “LTE-Advanced-LTE evolution towards IMT-Advanced Technology components”, 3GPP TSG RAN IMT Advanced Workshop, REV-080030, Apr. 7-8, 2008.    Non-patent document 2: “Initial Access Procedure for Asymmetric Wider Bandwidth in LTE-Advanced”, 3GPP TSG RAN WG1 Meeting #55, R1-084249, Nov. 10-14, 2008.